One conventional surface treatment machine, as disclosed in, e.g., Patent Literature 1, blast finishes an elongated members or workpiece. In such a conventional machine, if the elongated workpiece to be blast finished is, for instance, an H steel having an H-like cross section, the H steel is positioned in an H-like position in which its web surfaces are in their lateral positions, such that abrasives are projected on to the positioned H steel for surface treatment. In this case, because the upper side of the positioned H steel is formed almost like a slot, the abrasives that have been projected may remain therein. Therefore, this type of conventional machine requires that an H steel that has been surface treated should conveyed in its I-like position, in which the web surfaces are in their longitudinal position, to prevent the abrasives that have been projected from remaining on the treated H steel. However, this conveying position of the H steel to be conveyed lacks stability. In contrast, if the H steel is conveyed in its H-like position, as described above, the abrasives that have been projected may remain thereon.